1

EXERGY MODELING AND PERFORMANCE EVALUATION OF PULP AND PAPER

PRODUCTION PROCESS OF BAGASSE, A CASE STUDY

by

Mohammad Reza ASSARIa, Hassan BASIRAT TABRIZI

b, Ehsan NAJAFPOUR

c*,

Ali AHMADId and Iman JAFARI

e

a University of Jundi Shapor , Dezful ,Iran

b Amirkabir University of Technology Mech. Eng. Dept. Tehran, Iran

c* Engineering Department, Payame Noor University, Khorramabad, Iran,

ehsan_najafpour@yahoo.com

d Mechanical Engineering Department, Masjed Soleyman branch, Islamic Azad University, Masjed

Soleyman, Iran

e Mechanical Engineering Department, Dezful branch, Islamic Azad University, Dezful, Iran

Pulp and paper production industries are known as a renewable energy

technology. In this research, exergetic analysis of pulp and paper

production is presented. The system performance is evaluated based on

the data of Pars Paper Industrial Group (PPIG), Iran, which is given as

an illustrative example. An exergy destruction as well as exergy

efficiency relation is determined for each section of the system

components and the whole system to indicate the largest exergy losses

and possibilities of improvement. It is found that the largest exergy losses

occurred in the steam plant and soda recovery and these sections are

highly exergy inefficient. Further it is observed that with decrease of

excess air and preheating of inlet air the exergy efficiency of boilers is

increased.

Key words: bagasse, paper industry, exergy analysis.

Introduction

Pulp and paper industries have a high demand for both work and heat, which makes

them suitable for exergy studies. An exergy analysis (or second law analysis) has proven to be

a powerful tool in the simulation thermodynamic analyses of energy systems. In other words,

it has been widely used in the design, simulation and performance evaluation of energy

systems. It is employed to detect and to evaluate quantitatively the causes of the

thermodynamic imperfection of the process under consideration. Many researchers and

2

practicing engineers refer to exergy methods as powerful tools for analyzing, assessing,

designing, improving and optimizing systems and processes (Szargut et al. [1], Bejan et al.

[2], Dincer and Rosen [3]). Many exergy analyses for industrial processes have been reported. To

include the pulp and paper mills, Wall [4] discussed the simplicity and value of using the concept of

exergy when analyzing processes to develop conventions and standards within the field. Gemci and

Ozturk [5] performed exergy analysis of a sulphide-pulp preparation process in the pulp and paper

industry. Gong [6] studied exergy analysis of a pulp and paper mill and presented energy and exergy

concepts to a Swedish pulp and paper mill. Gui-Bing Hong et al. [7] analyzed the energy flow of the

pulp and paper industry in Taiwan. The potential technology options that were examined focus on how

to capture some of the energy currently lost in the processes and then identifying the areas with

energy-saving potential that could also have large impacts across a variety of industries. In addition,

the energy-saving potential of these options were evaluated. Sarimveis et al. [8] examined the

utilization of mathematical programming tools for optimum energy management of the power plant in

pulp and paper mills. The objective was the fulfillment of the total plant requirements in energy and

steam with the minimum possible cost. Cortés and Rivera [9] studied the optimization of a pulp and

paper mill with a cogeneration plant. The optimization included the exergy, exergoeconomics,

thermoeconomics and pinch analysis. The proposed methodology was useful in determining not only

the best plant operating conditions but also establishing the components or subsystems with the

highest irreversibilities. Further Marshman et al. [10] studied energy optimization in a pulp and paper

mill cogeneration facility. They presented an energy optimization algorithm for pulp and paper mill

cogeneration system. The algorithm was applicable to a number of popular mill configurations, power

sale contracts, and fuel purchasing scenarios. The method was also extended to address weather-

dependent cooling limitations encountered by a mill cogeneration facility, in which case an iterative

solution was proposed in order to maintain convexity of the optimization problem.

In this study, one of the Iranian pulp and paper industries is analyzed. Pars Paper Industrial

Group (PPIG) consists of two pulp mill and three paper mills and based material is bagasse. The main

objective of this study is to conduct an exergy analysis as a thermodynamic consideration. Parameters

such as fuel depletion ratio, relative irreversibility, productivity lack and exergetic factor are discussed

for better understanding and modeling. Analysis of all subsection that affected on the process is

performed to determine the most effective ways of improving the production of pulp and paper

process from bagasse.

System description

PPIG has two pulp and three paper mill. Its nominal capacity is 350 tones/day but at the time of

this study, the value of production paper was 146 tones/day. In the process of sugar production in Iran,

bagasse is a disposed material. However the process of making paper from wood uses more energy

than bagasse and bagasse is cheaper; it is an advantage to use bagasse as raw material. The production

process of pulp and paper in PPIG consists of the following stages as shown in fig. 1:

3

Depitting. Pit of bagasse separated by means of impact depitter hammer and screened.

Separated pit unused in process now, thus brought as a product. Depitted bagasse washed and

mixed with water and pumped to pulp mill.

Digester. Washed depitted bagasse pressed at first, so cooked in digester. In digester depitted

bagasse cooked with white liquor (100 kgm-3

) and steam (785 kPa, 170 oC). Lignin content in

bagasse dissolved in white liquor and useful pulp separated with lignin. Output of digester is

mixed pulp and liquor and enters to blue tank for continuing of reaction.

Figure 1. Production process in Pars Paper Industrial Group

DEPITTING

DIGESTER 1

CAUSTICIZING

5

DIGESTER 2

WASHING

SCREENING 1

WASHING

SCREENING 2

BLEACHING 1BLEACHING 2

PAPER MILL 1PAPER MILL 2PAPER MILL 3

BOILER 1

EVAPORATORS

SODA

RECOVERY

12 3

4

16 11

6

18

19

139

1014

17

28

24

33 30 29

40

41 37

36

6073

61 6574 78 48 5250 5163 6476 77

496275

82 83 84 8580

81

87

9293

91

98 97 96 9599100

104 103105

107

114

109

110

111

112

108

115116

113

118

117

119

120

BOILER 2

BOILER 3

ALSTOM

121

122

123

21

22

3134

2527

1215

3842

44

536679

89

8

7

23

20

26

3539

32

4345

47

82 83 84 8580

8168 69 70 7167

81

102

86

88

94

90

101

106

125

124

126

127

132

131

133

134

139

138

140

141

128

129

130

135

136

137

142

143

144

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Washing. Mixed pulp and liquor washed in three rotational screen washers with weak liquor

and warm water. Output weak black liquor of first washer pumped to recovery boiler for

recovery of white liquor. In screen unit, pulp passes in screen at high pressure and separated

residue lignin.

Bleaching. Some time brown pulp should be changed into white pulp. In order to do this

change, brown pulp is reacted in three stages with color, caustic, hypo and finally named

bleached pulp.

Evaporators. Weak black liquor should be concentrated so that it can be used in recovery

boiler. Evaporators include five effect (shell–tube) and concentrator in which weak black

liquor evaporated to 45% dry content.

Soda recovery. Strong black liquor resulting from evaporators is then evaporated in cyclone

evaporator to 60% dry content. Then strong back liquor enters the recovery boiler through the

black liquor burner. Organic substances are combusted in recovery boiler. Non- combusted

substances as melt enter the dissolving tank and they dissolve into weak wash liquor and

named green liquor. Soda recovery boiler generates high pressure steam (2945 kPa, 320 oC).

Causticizing. In causticizing unit green liquor converts to white liquor. Sodium carbonate is

reacted with lime (produce in lime kiln) at temperature of 100 oC. When reaction is complete,

sodium hydroxide is produced and calcium carbonate is removed.

Reaction in lime kiln follows:

Reaction in slacker is:

Paper mills. Three paper machines produce a number of different qualities paper. Saturated

steam enters the cylinder in paper machines and heat is transferred to pulp and dries it to form

paper. Almost 20% of all the pulp needed at mill is Kraft.

Steam boilers. Total steam in PPIG is provided with four oil boilers and a soda recovery

boiler.

In order to conduct the exergy method, it is necessary to descript the composition of bagasse. The

bagasse was analyzed for their composition and the data are presented in tab. 1.The heating value of

bagasse varies with moisture content and ash of bagasse. Considering the bagasse used in this process,

the heating value of bagasse is equal to 10500 kJkg-1

. Tab. 2 gives the assumed chemical

composition of the flows in the process.

Table 1. Average composition (ultimate analysis) of bagasse [11]

Substance H C O HHV (kJkg-1

) LHV (kJkg-1

)

Bagasse 6.8±1.3 45.3±1.3 45.4±1.7 16793±244 6484±568

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Table 2. Chemical composition of substances in the pulp and paper mill [4].

Substance H H2O C O Na2CO3 NaOH Na2S

Stripping liquor 0.6 85.8 4.7 3.9 0.9 2.5 1.6

Mixed liquor 0.9 76.2 7.4 6.4 1.7 4.5 2.8

Green liquor 80.8 14.0 5.2

Liquor 0.7 88.7 6.9 3.3 0.1 0.2 0.1

Pulp 0.8 87.1 6.3 5.8

Pulp & liquor 1.4 78.0 12.4 7.6 0.1 0.3 0.2

Paper/ Kraft liner 5.8 7.6 45.0 41.6

Waste paper 4.6 26.4 35.9 33.1

Waste liquor 0.9 77.2 7.5 6.2 1.5 4.1 2.6

Weak liquor 95.9 3.0 1.1

Black liquor 3.3 39.6 18.8 16.3 4.2 11.5 7.2

White liquor 83.2 3.1 8.4 5.3

Theoretical analysis

Unlike energy, exergy is not subject to a conservation law (except for reversible processes).

Rather exergy is consumed or destroyed due to irreversibility in any real process. The exergy

consumption during a process is proportional to the entropy created due to irreversibility associated

with the process. The total exergy of a system can be divided into four components, physical exergy,

kinetic exergy, potential exergy and chemical exergy as follows:

Only the physical and chemical exergy are considered in this study. Thus, the general exergy

rate balance can be expressed as follows (fig. 2):

The exergy destruction is synonym irreversibility and the exergy of waste includes the solid

and liquid waste, air emissions and follows:

ProcessExergy

input

Exergy of

product

Exergy

destruction

Exergy of

waste

Figure 2. Exergy balance

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The useful exergy is the exergy of the products. This can be calculated from the exergy

balance:

The specific physical exergy of flow i can be calculated from following equation:

Where is enthalpy, is entropy and the subscript zero indicates properties at the dead state

of and .

The chemical exergy of substance calculated as [12]:

Where is the mole fraction of component j , each component has molar and the universal gas

constant. Chemical data of substances can be taken from the literature (see [1]).

The exergy of the mixture is determined by its nature. In an ideal mixture the enthalpy can be

calculated as the sum of the enthalpies of its component. The entropy of a mixture, on the other hand,

is determined by its nature. The entropy of mixtures is [4]:

Exergy is lost when separated substances are allowed to form an ideal mixture. The mixtures

occurring in this analysis are rather non-ideal mixtures. However, there is no general theory or

unequivocal concept for non-ideal mixtures. Data on specific heats are generally only available for

pure elements and for specific chemical compounds such as oxides. Thus, the specific heat of a

mixture is assumed to be the sum of the specific heat of the substances in relation to their proportion.

This will generate incorrect values of thermal energy and exergy for mixtures where new phases

appear. However, the impact on the final result from these errors is considered to be negligible in

comparison to other errors, e.g. in the data for material flows and temperatures [4]. Change of entropy

calculated for solids and liquids from:

In addition, for ideal gas:

The efficiency of the process is then defined as the useful exergy of the total input exergy:

The exergy loss is can be calculated as:

For thermodynamics analysis of system, the following parameters are used (see [12, 31]):

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For fuel depletion ratio:

Relative irreversibility:

Productivity lack:

Exergetic factor:

Results and discussion

The parametric analysis is performed to evaluate the performance- in terms of exergy- of the

sub-process in Pars Paper Industrial Group (PPIG) and also to indicate the largest exergy losses and

possibilities to improve them. The Pars Paper Industrial Group (PPIG) consists of two pulp mill and

three paper mills and based material is bagasse. Tab. 3 illustrates the description of the plant’s flow

and their thermodynamic properties. The material flows of every sub-process are given in ton per ton

of produced paper and the exergy flows in . In this study 1 kJ electricity is used as 1 kJ

input energy to the process.

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Table 3. Exergy flow and other properties in PPIG (for state numbers refer to fig. 1)

State No.

In Fig. 1 Fluid

Mass flow rate

Temperature

Pressure

kPa

Exergy flow

1 Raw bagasse 2.69 25 26605.89 2 Water 23.52 35 34.34 3 Electricity - 753.3 4 Depitted bagasse 2.33 25 23999 5 Pit 0.23 25 2185 6 Water 9.09 30 1.54 7 Waste water 14.51 30 2.32 8 Waste bagasse 0.13 25 1186.88 9 Steam 0.78 170 785 kPa 630.41 10 Caustic 0.97 25 1415.61 11 Bagasse 0.8 25 8240 12 Electricity - - 162.57 13 Steam 1.6 170 785 kPa 1309.72 14 Caustic 1.85 25 2699.87 15 Bagasse 1.53 25 15759 16 Electricity - - 169.31 17 Pulp & liquor 2.4 100 10200 18 Steam 0.1 150 100 kPa 49.02 19 Waste 0.05 100 24.51 20 Pulp & liquor 4.28 100 18190 21 Steam 0.6 150 100 kPa 294.15 22 Waste 0.1 150 49.02 23 Pulp & liquor 2.4 70 10200 24 Water 3.6 75 51.66 25 Electricity - - 325.15 26 Pulp & liquor 4.28 70 18190 27 Water 5.5 75 93.78 28 Electricity - - 470.18 29 Pulp 2 60 6202 30 Black liquor 3.7 60 4297.58 31 Waste 0.3 60 58.69 32 Pulp 3.75 60 11628.75 33 Black liquor 4.51 60 5238.41 34 Waste 1.52 60 147.95 35 Brown pulp 50 36 hypo 75 37 Saturated Steam 0.24 130 270.1 kPa 151.21 38 Electricity - - 140.63 39 Brown pulp 3.67 50 11380.67 40 hypo 0.72 75 9.1 41 Saturated Steam 0.48 130 270.1 kPa 280.93 42 Electricity - - 198.22 43 White liquor 1.42 40 4403.42 44 Waste materials 0.94 75 82.41 45 White liquor 3.27 40 10140.27 46 Waste materials 1.6 75 748.88 47 Pulp 1.83 35 2674.83 48 Waste paper 0.04 45 597.4 49 Steam 2.26 140 360 kPa 1521.4 50 Water 8.73 35 9.25 51 Water 0.9 55 5.34 52 Brought pulp 0.05 35 1108.85 53 Electricity - - 640.69 54 Paper 0.36 45 7983.72 55 condensate 1 100 34.36 56 Water 4.05 35 2.83 57 Waste water 6.24 25 0 58 Water 0.9 45 2.41 59 Waste condensate 1.26 100 43.29 60 Pulp 1.51 35 4682.51 61 Waste paper 0.05 45 724.25 62 Steam 1.76 140 360 kPa 1185.06 63 Water 7.11 35 7.91 64 Water 0.8 55 4.74 65 Brought pulp 0.04 35 887.08 66 Electricity - - 714.42 67 Paper 0.29 45 6431.33 68 condensate 1 100 100 kPa 34.36 69 Water 3.25 35 2.27 70 Waste water 5.17 25 0 71 Water 0.8 45 2.14

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Table 3 (continued)

State No.

In Fig. 1 Fluid

Mass flow rate

Temperature

Pressure

kPa

Exergy flow

72 Waste condensate 0.76 100 100 kPa 26.11 73 Pulp 1.68 35 5209.68 74 Waste paper 0.02 45 289.7 75 Steam 2.39 140 360 kPa 1609.26 76 Water 8.4 35 7.16 77 Water 0.4 55 2.37 78 Brought pulp 0.04 35 887.08 79 Electricity - - 975.65 80 Paper 0.35 45 7761.95 81 condensate 1.8 100 100 kPa 61.85 82 Water 3.53 35 2.47 83 Waste water 6.66 25 0 84 Water 0.4 45 1.07 85 Waste condensate 0.19 100 100 kPa 6.52 86 Stripping liquor 8.2` 60 9536 87 Water 1.99 30 40.59 88 Steam 2.62 141 375 kPa 1770.07 89 Electricity - - 89.77 90 Strong black liquor 1.56 102 8582.4 91 Water 1.99 50 10.65 92 Waste condensate 7.19 60 20 kPa 58.89 93 condensate 2.08 90 70 kPa 55.83 94 Strong black liquor 1.56 95 8584.2 95 Water 6.83 120 354.66 96 Steam 1.2 207 1075.44 97 Fuel oil 0.36 65 1473.8 98 Air 8.48 25 0 99 Weak wash liquor 2.21 55 376.25 100 Electricity - - 601.95 101 Green liquor 1.7 95 1810.53 102 Steam 5.67 345 2945 kPa 6153.76 103 Exhaust gas 10.4 119 479.06 104 Water 0.7 210 635.74 105 Waste 2.17 274 594.58 106 Green liquor 1.7 90 1810.53 107 Water 1.24 50 5.11 108 Natural gas 0.05 20 193.83 109 sodium carbonate 0.13 65 1.23 110 Air 1.16 25 0 111 Water 0.19 25 0 112 Electricity - - 193.8 113 White liquor 0.8 90 1167.51 114 Weak wash liquor 1.72 55 296.23 115 Exhaust gas 1.53 536 451.61 116 Waste material 0.42 65 68.53 117 Water 0.86 108 33.15 118 Fuel oil 0.08 60 3274.72 119 Air 5.62 25 0 120 Electricity - - - 71.8 121 Steam 0.69 250 2000 kPa 616.7 122 Exhaust gas 5.7 188 669.81 123 Waste water 0.17 160 17.97 124 Water 1.11 108 43.29 125 Natural gas 0.07 20 3184.87 126 Air 2.1 25 0 127 Electricity - - 92.43 128 Steam 0.95 250 2000 kPa 840.75 129 Exhaust gas 2.17 115 201.42 130 Waste water 0.16 164 46.45 131 Water 0.81 108 31.59 132 Natural gas 0.06 20 2725.75 133 Air 1.89 25 0 134 Electricity - - 131.7 135 Steam 0.71 250 2000 kPa 628.3 136 Exhaust gas 1.95 126 147.65 137 Waste water 0.1 95 11.99 138 Water 9.98 120 570.72 139 Natural gas 0.55 20 25019.12 140 Air 9.49 25 0 141 Electricity - - 312.98 142 Steam 8.91 250 2000 kPa 8524.28 143 Exhaust gas 10.04 224 1402.79 144 Waste water 1.07 95 137.08

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The exergy efficiency, exergy destruction rate and some thermodynamic parameters for all the

sub-processes are given in tab. 4. The highest exergy destruction occurred in soda recovery with

relative irreversibility value of 33.98%. It is followed by Alstom boiler with 29.81%. The lowest

exergy efficiency is in boiler 1. It is followed by boiler 3, boiler 2, soda recovery and Alstom boiler

with 18.24%, 21.75%, 25.3%, 28.73% and 32.91% respectively.

Table 4. Exergetic and thermodynamics analysis data provided for sub-processes

Exergetic

factor

Productivity

lack

Relative

Irreversibility

Fuel

depletion

rate

Exergy

Efficiency

Exergy of waste

Exergy

destruction

Exergy of

the Product

Exergy

of the Fuel

component

Item

no.

13.15 0.01 0.03 0.0091 95.59 1189.2 18.97 26185.45 27393.62 Depitting 1

5.02 0.12 0.33 0.0841 98.09 24.51 175.06 10249.02 10448.59 Digester 1 2

5.08 0.01 0.03 0.0089 99.27 58.69 18.54 10499.58 10576.81 Washing 1 3

2.75 0.84 2.33 0.59 76.94 82.47 1237.42 4403.42 5723.31 Bleaching 1 4

9.57 0.95 2.64 0.67 92.71 49.02 1404.73 18484.15 19937.9 Digester 2 5

9.00 1.17 3.25 0.83 90.01 147.95 1724 16867.16 18739.11 Washing 2 6

5.7 0.66 1.84 0.47 85.43 748.88 979.77 10140.27 11868.92 Bleaching 2 7

4.58 0.99 2.77 0.71 84.08 49.53 1469.33 8020.91 9539.77 Paper machines 1 8

3.94 1.15 3.21 0.82 78.82 31.28 1706.73 6467.96 8205.97 Paper machines 2 9

4.31 0.77 2.15 0.55 87.14 13.18 1141.45 7826.27 8980.9 Paper machines 3 10

5.49 1.85 5.13 1.31 75.57 59.89 2727.66 8648.88 11436.43 Evaporators 11

13.31 12.21 33.98 8.67 28.73 1709.38 18051.83 7964.29 27725.5 Soda recovery 12

1.06 0.15 0.42 0.11 66.4 520.14 221.36 1463.74 2204.5 Causticizing 13

1.62 1.4 3.91 1.0 18.25 687.72 2075.25 616.7 3379.67 Boiler 1 14

1.59 1.51 4.2 1.07 25.3 247.87 2232.47 840.25 3320.59 Boiler 2 15

1.39 1.42 3.95 1.01 21.75 159.64 2101.1 628.3 2889.04 Boiler 3 16

12.44 10.71 29.81 7.6 32.91 1539.87 15838.67 8524.28 25902.82 Alstom boiler 17

The digester 1 and digester 2 are considered section digester. Similarly, washing screening 1

and washing screening 2 section washing screening, bleaching 1 and bleaching 2 section bleaching,

paper mill 1, paper mill 2 and paper mill 3 section paper mill, Boiler 1, Boiler 2, Boiler 3 and Alstom

Boiler section steam plant are considered.

The exergy flow diagram is drawn in fig 3. This flow diagram includes utilized and unutilized

outflows for all sub process in PPIG. It indicates that 73.73% (corresponding to about 60850.14

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) of the total exergy entering the system is lost, while 26.27% is utilized. The highest exergy

loss occurs from the steam plant with 29.85% (corresponding to about 24881.87 ) of the total

exergy input due to irreversibility of combustion and heat transfer. The second largest exergy loss

(accounting for 23.7%) occurs from soda recovery. The steam plant and soda recovery have

considerably larger exergy losses due to the production of steam.

Figure 3. Exergy flow diagram for pulp and paper industry

In this study the exergy efficiency of main section of pulp and paper production is compared

with SCA-Munksund pulp and paper mill [4] and Skoghall mill [6] and is shown in tab. 5. Exergy

efficiency values were obtained 95.59% for the depitting, 79.47% for the digester, 93.35% for the

washing, 82.67% for the bleaching, 83.5% for the paper mill, 29.9% for the steam plant, 69.47% for

the evaporator, 28.37% for the Soda recovery and 66.4% for the causticizing. These processes

generate steam, so the exergy efficiency is low. The main cause of this low efficiency is the

irreversibility of combustion and of heat transfer in the steam generator due to the low temperature

output. The difference in temperature between the combustion gases and the working fluid is very

large. Thus, in principal, it is possible to add a process that utilizes this temperature difference.

Furthermore, the exergy efficiency of soda recovery and the steam plant are lowest and immediate

efforts to improve the process should therefore be focused on these processes.

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Table 5. Comparison exergy efficiency of PPIG with SCA-Munksund [4] and Skoghall [6]

Skoghall SCA-

Munksund PPIG Section

97% 99% 95.59% Depithing

85% 99.7% 79.47% Digester

79% 99.1% 93.35 Washing

94% - 82.67% Bleaching

89% 86.2% 83.5% Paper mill

29% 31.3% 29.9% Steam plant

97.1% 97.1% 69.47 Evaporator

30% 36.3% 28.73% Soda recovery

87% 87.4% 66.4% Causticizing

Boiler 1 and soda recovery are using fuel oil and boiler 2, boiler 3 and Alstom boiler are using

natural gas. Exergy losses as waste flows are predominantly exhaust gases and damp air that are

strongly linked to the steam plant and soda recovery. The percent excess air in combustion of natural

gas and fuel oil is efficient parameter to optimize exergy efficiency and decrease exergy losses in the

process. Then, according to exhaust gas analysis of boilers the optimal decrease of excess air for fuel

oil boilers and natural gas boilers are 25% and 10% respectively. Tab. 6 indicates the effect of

decrease of excess air on efficiency of boilers. With decrease of excess air for boilers increases the

exergy of boiler 1, boiler 2, boiler 3, Alstom boiler and Soda recovery i.e. 16%, 3%, 2%, 1%, 2%,

respectively.

Table 6. Effect of decrease of excess air on efficiency of boilers

Component

Initial percent

excess air

(%)

Initial

combustion eff.

(%)

Decrease of

excess air

(%)

New

combustion eff.

(%)

boiler 1 280 67.7 25 88.5

boiler 2 100 75.4 10 87

boiler 3 100 71 10 87.5

Alstom boiler 12.7 81.9 10 87.5

Soda recovery 33 84 25 87.5

Other efficient parameter for optimizing exergy efficiency is preheating of inlet air of boilers.

It is observed with preheat air up to 100°C to increase inlet air temperature of boilers increases the

exergy efficiency. Further increases the efficiency of boiler 1, boiler 2, boiler 3, Alstom boiler and

Soda recovery i.e. 3%, 4%, 4%, 2%, 2.5%, respectively.

By preheating combustion air and by decreasing excess air in the boilers it will be possible to

save some fuel while generating the same quantity of steam. Tab. 7 illustrates the annual fuel saving

for the operation.

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Table 7. Annual fuel saving in boilers

Component Fuel

Average Fuel

consumption

( )

Fuel saving

( )

boiler 1 fuel oil 0.8 824.1

boiler 2 natural gas 700 525660.8

boiler 3 natural gas 632.2 581133.8

Alstom boiler natural gas 3895.3 2001872.6

Soda recovery fuel oil 2.26 631.8

Conclusions

An exergetic analysis and performance evaluation of pulp and paper production in Pars Paper

Industrial Group (PPIG) in Iran is presented. In order to determine the most effective procedure to

improve the production of pulp and paper process from bagasse, all subsection that affected on the

process is analyzed. The highest exergy losses are occurred in the steam plant and soda recovery. The

steam plant and soda recovery have considerably larger exergy losses due to the production of steam.

Thus, it is possible to develop better technology for them. With decrease of excess air and preheating

of inlet air, exergy efficiency of steam plant and soda recovery can be increased. Further annual fuel

saving in boilers is estimated.

Nomenclature

- Specific heat, [Jkg-1

K-1]

- Constant pressure specific heat, [Jkg-1

K-1

]

- Specific exergy, [kJkg-1

]

- Exergy rate, [kJs-1

]

- Exergetic factor, [%]

- Exergy rate of the fuel, [kJs-1

]

- Specific enthalpy, [kJkg-1

]

- Rate of irreversibility, [kJs-1

]

- Pressure, [Pa]

- Exergy rate of the product, [kJs-1

]

- Molar gas constant (8.314), [kJkg-1

mol-1]

- Specific enthalpy, [kJkg-1

K-1

]

- Entropy rate, [kJs-1

]

- Temperature, [K]

- Mol fraction in the steam

Greek letters

- Fuel depletion rate, [%]

- Exergy losses

- Molar exergy of each component

14

- Exergy efficiency, [%]

- Productivity lack, [%]

- Relative irreversibility, [%]

Subscripts

- Destroyed (destruction)

- Generation

- Flow

- Inlet

- Component

- Successive number of elements

- Outlet

- Total

- Dead (reference) state

Reference

[1] Szargut, J., Morris, D. R., Steward, F. R., Exergy Analysis of Thermal, Chemical, and

Metallurgical Processes, New York: Hemisphere Publishing, 1988

[2] Bejan, A., Tsatsaronis, G., Moran, M., Thermal Design and Optimization., Wiley: USA, 1996

[3] Dincer, I., Rosen, M. A., Exergy: energy, environment and sustainable development, Elsevier,

2007

[4] Wall, G., Exergy flows in industrial processes, International Journal of Energy, 17 (1988),

pp. 197-208

[5] Gemci, T., Ozturk, A., Exergy analysis of a sulphide-pulp preparation process in the pulp and

paper industry, Energy Conversation and Management, 39 (1998), pp. 1811–1820

[6] Gong, M., Exergy analysis of pulp and paper mill, International Journal of Energy Research,

29 (2005), pp. 79-93

[7] Gui-Bing Hong., Chih-Ming Ma., Hua-Wei Chen., Kai-Jen Chuang., Chang-Tang Chang.,

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